Well, it's a while since, but if you did not have any problems so far, I would not worry too much
about Security. Still, PHP is moving up, and mySql needs to be changed to MySqli, besides of
the need of a responsive Theme, to meet today's Viewer Requirements.

But I take the opportunity, to again explain the whole Situation a little more detailled, It save's me
from repeating it ever again...
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Upgrading to a later Main Version OC usually means, to change everything, exept
for existing Product and Theme Background Images, and some Content of a DB.
Everyting else needs to be replaced, and one should NEVER TRY, to INSERT a later
Version Software into an existing older Version Shop Directory, full of old Code and
no longer VALID Image and Code Directories !
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Strictly technically, you could make a full Test Installation by use of OC v.1.5.6.5_rc, the latest
and most perfect (in-)official 1.5.6.x Series Release:Opencart-1.5.6.5_rchttps://github.com/IP-CAM
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And then just try to RESTORE a downloaded old Shop DB Backup, to find out, if everything still
works as planned. But if you have some Custom Extensions on Board, eventually adding some Custom
Content to a DB, you might need a paid Service like this, to upgrade your 1.5.5.1 DB to v.1.5.6.5_rc:Opencart Migration & Remote Upgrade Toolhttp://www.pm-netti.com/oc-upgrade-tool.html
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And you can also get a free original OC v.2.x responsive Bootstrap3-Theme Extension, it will make
OC v.1.5.6.x Engines capable of using a range of free early Version 2.0.x.x Bootstrap Theme Styles,
partly done by only exchanging the default stylesheet.css with another one, as you can
see here:http://www.opencart.li/themes.html
Famous Peku's great free OC2-to-OC1.5 Theme Extension is downloadable from here:OC 2 Theme to Oc 1.5 http://www.pm-netti.com/opencart/others/oc2_theme.html
It also contains OcMod, the OC v.2+ Version Step-sister of VqMod, for some reason ,
but this can be switched off later again, since it makes no sense, to have a second CACHING Routine
activated, besides VqMod, and running, if (officially) no 1.5.6.x OcMods exist for... Or then,
one could easy rewrite existing VqMod's to OcMod's, to have and enjoy the rather exclusive OC-2+
like OcMod Feeling !
I once even created an OcMod Editor, among a few other things, just in Case, one's looking for...
Performance-wise, there is no difference between VqMod and OcMod, one should better just not use
them both, it can make many things much more complicated, like everywhere, where more than One
is in charge of something specific -- whatever it might be...
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Just to give you some Ideas, if you plan, to further use your familiar OC Administration Layout,
Functions, and the giant Reservoir on free Knowledge. And you might use some Mod's, wich would no
longer function, if you move up further than 1.5.6.5 in OC Versions. Otherways, you'll need to get your
Database upgraded, to match later Versions again, and if you want additional Extensions, you'll have to
get new one's, in most any case.
---WICH DOES NOT MEAN, that all of your existing Extensions will still function correctly in a modern
responsive v.1.5.6.5_rc Bootstrap-3 OC v.2 Layout. Most everything, related with the visual Design, by example,
some additional 'Information' on a Product Page, likely needs to be rewitten a little, to match again the new Theme
File Code, Tag, or whatever, serving as ANCHOR for VqMod Routines. Just to have it mentioned too!
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And to complete this, famous PEKU also created a very nice OpenCart 1.5.6.5 EDGE Versionhttps://github.com/pekka2/Opencart-1.5.6.5-Edge
by use of a v.1.5.6.5_rc Engine and the OC-2 Theme, as DEFAULT Setup. But unfortunately, it still has a few little
minor missings, and for the time beeing, I guess, it's 'easier' to install the default _RC Version and add PEKU's
OC2 to OC 1.5 Theme Extension, even easier to find the misses, since much of it is placed in one VqMod File.
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You see, some work will be involved, there is no way around it. And because of that, one should always
create a separate TEST Environment, and never play around on a working Shop. Only after it works in full,
a Test Shop Directory should renamed to the default Shop Sub, and the former Shop Software does not any
harm, if it stays on a Server still for a while, just to make sure, you online presence will not be interrupted,
while changing Versions.
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PEKU's 1.5.6.5 EDGE Software should be installable up to PHP 7.0.xx (max!), But the Github Default
1.5.6.5_r c Install Code will not be accepted by PHP-7. In such a case, one could contact me, to get working
PHP 7.0.xx Installation Code, OR THEN, install OC with a 5.x PHP Version, the Shop will WORK under PHP 7-0.xx!
The same would apply, if PEKU's Install Routine should not function as planned, in order to get my working
Custom Install Routine.
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Good Luck!
Ernie
---OpenCart 1.5.5 Bug Threadhttp://forum.opencart.com/viewtopic.php?f=161&t=93332
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